Abstract
P91 ferritic/martensitic and AISI 304L austenitic stainless steels were hot dip aluminized (HDA) in 99.9% pure aluminum in a pit type vertical furnace at three different temperatures i.e. 750, 800 and 850 degrees C for 1 to 10 min. Evolution of interface morphology, type and distribution of phases and growth kinetics of the reaction zones were studied using a variety of experimental techniques. Though similar intermetallic compounds formed in both steels, their distribution, morphology and growth kinetics were distinctly different. In P91 F/M steel, aluminized surface adjacent to the substrate had wide Fe2Al5 layer with serrated morphology containing high volume fraction of 2-3 mu m sized Cr rich intermetallic phases. Width of FeAl3 phase present adjacent to this layer did not show much variation with HDA conditions. Above FeAl3, on the surface, the pure Al top coat contained nonequilibrium phases. Compared to P91 steel, width of the aluminized layer in 304L SS was less (35 +/- 5 mu m vs 120 +/- 15 mu m at 800 degrees C-10 min) and the Fe2Al5 layer had a planar interface with the substrate. Optimum temperature-time combination to get thin, uniform, defect free surface aluminide layer in P91 F/M and 304L steels were found to be 750 degrees C-2 min and 800 degrees C-1 min respectively. Growth kinetics of surface aluminide layers in both steels were studied, kinetic parameters were determined and compared with information available in literature.
NSTL
Elsevier